Stephenie Meyer achieved youth culture fame overnight with her supernatural “Twilight” novels and films. But immortality? As the makers of Livestrong yellow wristbands or “High School Musical” can attest, that’s harder to come by.

Meyer’s latest, “The Host,” blends teen romance and science fiction. In its strange new world, advanced, peaceable extraterrestrials have commandeered the minds of most of Earth’s human population. This case of global possession has a benign face. Earth 2.0 is without war, hunger, greed and cancer. Humans retain their physical form, dress impeccably, drive silver luxury sports cars and live in elegant mid-century modernist digs. Unfortunately, the aliens want to ease Homo sapiens aside permanently, convinced that they can do a better job of running our planet.

An alien intelligence named Wanderer inhabits Earth girl Melanie Stryder. Even after she’s implanted with her new “soul,” defiant Melanie (Saoirse Ronan) doesn’t knuckle under. Her will and awareness survive, gradually revealing thoughts and memories to Wanderer (Wanda for short). The battle to control Melanie’s body is a psychic pillow fight, with Ronan voicing both sides of the running argument in her head. Like mismatched bunkies at sleepaway camp, they squabble, then learn to coexist, ultimately forming an emotional connection.

Melanie convinces the resistant Wanderer that they must flee to the desert cabin of Uncle Jeb (William Hurt) and Aunt Maggie (Frances Fisher). Evading the alien security chief Seeker (Diane Kruger) and her crew, Melanie/Wanda discover remote caves sheltering the handful of remaining humans. Among them are Melanie’s boyfriend Jared (Max Irons) and his fellow freedom fighter Ian (Jake Abel), who falls for Wanda. With two identities in a single body, our heroines find themselves in a two-way love triangle, then a three-person love quadrangle. And Bella Swan thought she had a tangled love life!

Writer/director Andrew Niccol (“The Truman Show,” “Gattaca”) does a capable job with the physical aspect of the production. The sleek environments the aliens inhabit evoke a sense of purity that is both soothing and creepy. They shop at a place titled “Store” where goods are abundant, but displayed in sterile packaging with no visual differentiation between items. The humans’ spaces are wet (soggy waterfront cabins) or arid (sun-blasted southwestern rock formations). There’s a battle of cold Design Within Reach conformity vs. shaggy thrift-store diversity in every shot.

But there’s only so much value that Niccol’s slick presentation can add to Meyer’s shallow material. Ace stuntwork notwithstanding, the movie lacks a sense of danger and urgency. The emotional groundwork for a compelling conflict is missing. Given that the aliens are generally a peace-loving lot, their pursuit of the rebels never ignites much anxiety. Kruger makes her character the most “human” of the aliens, with a duplicity and rash temper not seen in her beige comrades. Frankly, they’re creampuffs.

Open Road Films

Saoirse Ronan and Jake Abel in “The Host.”

Only one scene admits the absurdity of the situation as Melanie/Wanda steals a pallet full of food from “Store” by wheeling it directly past the placid staff and out the door. It’s a nice gag in a film mostly bereft of levity or self-awareness. How could they have ignored the comic gold mine of a crazy-acting teen girl with two brains? I wouldn’t put money on this mishmash of “Invasion of the Body Snatchers” and “Love Story” scoring with fantasy fans. They’ll probably hang on until fall for the next installment of the dramatically superior “Hunger Games.”

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